Carbon fiber exhibits superior mechanical strength, electric conductivity, heat conductivity and other properties compared to glass fiber and has therefore been used in many applications including plastic reinforced materials, gas storage materials, and electrode materials.
Methods of manufacturing carbon fiber that are well-known in the art include carbonization of organic fiber such as synthetic fiber or petroleum pitch fiber, and thermal decomposition of a hydrocarbon such as benzene or methane under the presence of catalyst to produce carbon fiber (gas phase method). The gas phase method is the most suitable method for continuous mass production.
Manufacturing of carbon fiber by the gas phase method is usually effected by either one of the following methods: 1) A first manufacturing method wherein in a high-temperature reactor a gaseous hydrocarbon introduced into the reactor is allowed to contact a catalyst fixed on a substrate; and 2) a second manufacturing method wherein a raw material including a hydrocarbon and a catalytic component is introduced into a high-temperature zone of a reactor in the form of gas or liquid. The first manufacturing method does not lend itself for continuous production because it requires the step of taking out produced carbon fibers by removing the catalyst fixed-substrate. On the other hand, the second manufacturing method lends itself for continuous production because it does not require such complexity. Especially, among different types of the second manufacturing method, a manufacturing method that involves pulse introduction of a raw material liquid (Liquid Pulse Injection technique; LPI technique) can produce highly dense catalyst fine particles which are advantageous for the production of carbon fiber.
As examples of the second manufacturing method (LPI technique), PTLs 1 to 3 disclose a rapid and efficient manufacturing method of carbon fiber by pulse introduction of a raw material liquid containing a hydrocarbon and a catalytic component into a reactor in which a carrier gas flows continuously. PTL 4 discloses a continuous manufacturing method of carbon fiber by introducing a raw material liquid containing 15 mol % or more of methane into a high-temperature zone having a temperature of 1,100° C. to 1,500° C. for efficient use of catalyst.